The present invention relates to multiplexed electronic control systems and in particular to multiplexed control systems for motor vehicles.
With the increasing sophistication of motor vehicles, several electronic control modules are used to control the different systems of the vehicle, for example: engine control module (ECM); transmission control module (TCM); antilock braking module (ABS) and instruments and driver information module (INST). These modules monitor various control inputs and operational parameters of the related system and control the system accordingly. For example, the ECM may monitor accelerator pedal depression to control the ignition and fuel systems of the engine. The ECM may also monitor engine speed, torque and other operating parameters of the engine to optimise the performance of the engine.
Some of the controls or operating parameters monitored by one module may also be required by one or more of the other modules. For example, engine speed which is monitored by the engine control module may also be required by the transmission control module, antilock braking module and the instruments and driver information module. Furthermore, wheel speed which is monitored by the antilock braking system module may be used by the engine control module and transmission control module for traction control purposes.
The various modules are consequently interconnected in a network so that information may be interchanged between the modules and the modules can perform their functions in an integrated manner. The modules are preferably interconnected by a twisted wire pair, the interchange of information being carried out by the CAN protocol in accordance with ISO/DIS 11898 `Road Vehicles--Interchange of Digital Information--Controller Area Network (CAN) for High Speed Communication`.
A problem with networks of this type is that if one of the modules malfunctions, it may also affect the correct operation of the other modules to which it provides information. It is consequently necessary to provide means for warning of such faults, so that the network can be made aware of a problem and action can be taken to mitigate the consequences.
One method of doing this would be for all modules to monitor all of the information transmitted by all of the other modules. This however, would use excessive processing and memory resources and as most modules will only require a relatively small amount of the information transmitted, would be extremely wasteful.